Powertrain of a motor vehicle and method for controlling said powertrain

ABSTRACT

The power train ( 1 ) includes a controlled drive source ( 3 ), a clutch ( 6 ), an automatically shifting transmission ( 7 ) and a data transmission device ( 2 ). The power train contains an additional drive source ( 12 ) and is fitted with a control system by means of which a correction value (K pid) for the drive source torque is generated on the basis of the comparison of the actual behavior of the drive train with a modeled behavior of a drive train fitted with a hydrodynamic torque converter. The behavior of a torque converter is simulated by a regulating circuit ( 21 - 27 ).

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/840,499 filed May 6, 2004, now U.S. Pat. No. 7,099,762 which is acontinuation of copending International Application No. PCT/DE02/04093filed Nov. 4, 2002 which designates the United States, and claimspriority to German application no. 101 55 433.8 filed Nov. 12, 2001, theentire contents of which are hereby incorporated in their entirety byreference.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a powertrain of a motor vehicle which comprisesa controlled power source, a clutch, an automatically shiftedtransmission and a data transfer system enabling data to be exchangedbetween the component parts of the powertrain.

DESCRIPTION OF THE RELATED ART

Motor vehicles having an internal combustion engine, an automatictransmission and a hydrodynamic torque converter (hereinafter alsoreferred to as HTC) exhibit a starting behavior which, because of theincreased torque provided by the HTC, more specifically in the case of alow converter input/output speed ratio, makes faster vehicleacceleration possible (Fachkunde Kraftfahrzeugtechnik (TechnicalInformation: Automotive Engineering), published by Europa-Lehrmittel,26th edition 1999, Haan-Gruiten, pp. 403-404). The increased torqueprovided by the torque converter is therefore experienced as favorableby the motor vehicle driver.

Motor vehicles having a powertrain containing a crankshaftstarter/generator (hereinafter also referred to as ISG), an internalcombustion engine and an automated manual transmission, but nohydrodynamic torque converter, are only provided with a friction clutchto decouple the crankshaft rotation from the wheel rotation, said clutchbeing unable to increase the driving torque above the torque at thecrankshaft.

SUMMARY OF THE INVENTION

The object of the invention is to create a powertrain of a motor vehicleequipped with a friction clutch which has a starting behavior like thatof a motor vehicle provided with a hydrodynamic torque converter.

The object of the invention can be achieved by a motor vehiclepowertrain comprising a controlled power source, a clutch, anautomatically shifted transmission and a data transfer system enablingdata to be exchanged between the component parts of the powertrain, anadditional power source, and a control system for producing a correctionvalue for the power source torque on the basis of a comparison of thereal behavior of the powertrain with a modeled behavior of a powertrainprovided with a hydrodynamic torque converter.

The controlled power source can be an internal combustion engine. Theadditional power source can be a crankshaft starter/generator, theclutch can be implemented as an automatically actuated friction clutch,and there can be provided a feedback loop for simulating the behavior ofa torque converter. The control system may contain a conversion blockfor converting a required wheel torque to a crankshaft torque on thebasis of the correction value, and a correction device in which thecorrection value for the torque is generated. The control system mayhave a torque divider for splitting the power source torque between thepower source and the additional power source. The control system mayhave an observer block which represents a model of a powertrain having ahydrodynamic torque converter and is used to calculate a vehicle speedcorresponding to the speed assumed by a comparable motor vehicleprovided with a hydrodynamic torque converter and an automatictransmission in response to the same driver input. The vehicle speed canbe determined in accordance with the following equation

$V_{Fahrzeug} = {r_{reifen}*{\int{\frac{\lbrack {{( {{tq}_{eng} + {tq}_{ISG}} )*\mu_{HTC}*i_{AT}*i_{Diff}} - {tq}_{Fahrwid}} \rbrack}{{theta}_{kfz}}{\mathbb{d}t}}}}$where:

-   -   μ_(HTC) is the increased torque provided by the hydrodynamic        torque converter    -   i_(AT) is the gear ratio of the automatic transmission    -   i_(Diff) is the gear ratio of the differential    -   r_(reifen) is the tire radius    -   theta_(kfz) is the moment of inertia of the vehicle and    -   tq_(Fahrwid) is the rolling resistance    -   (tq_(eng)+tq_(ISG))′ is the theoretical driving torque.

The required driving torque for the powertrain can be determinedaccording to the following equation

$( {{tq}_{eng} + {tq}_{ISG}} ) = {\frac{{tq}_{wheel}}{{slip}_{clutch}*i_{AMT}*i_{Diff}}*k_{pid}}$where:

-   -   i_(AMT)=i_(AT) is the gear ratio of the automatic transmission    -   i_(Diff) is the gear ratio of the differential    -   k_(pid) is the correction factor    -   slip_(clutch) is the clutch slip    -   tq_(eng) is the actual torque of the internal combustion engine    -   tq_(ISG) is the actual torque of the crankshaft        starter/generator    -   tq_(wheel) is the wheel torque.

The object can also be achieved by a method for controlling powertraincomprising a controlled power source, a clutch, an automatically shiftedtransmission and a data transfer system enabling data to be exchangedbetween the component parts of the powertrain, an additional powersource, and a control system, the method comprising the step ofproducing a correction value for the powertrain torque on the basis of acomparison of a real behavior of the powertrain with a modeled behaviorof a powertrain provided with a hydrodynamic torque converter.

A conversion block performs a conversion of a required wheel torque to apowertrain torque on the basis of the correction value and that thepowertrain torque is divided between the power source and the additionalpower source. A demanded torque can be converted to a necessary torqueat the crankshaft of the power source using the gear ratios of thepowertrain components. The method may comprise the step of splitting thepower source torque between the power source and the additional powersource by a torque divider. The method may also comprise the steps ofrepresenting a model of a powertrain having a hydrodynamic torqueconverter by an observer block and using the model to calculate avehicle speed corresponding to the speed assumed by a comparable motorvehicle provided with a hydrodynamic torque converter and an automatictransmission in response to the same driver input. The vehicle speed canbe determined in accordance with the following equation

$V_{Fahrzeug} = {r_{reifen}*{\int{\frac{\lbrack {{( {{tq}_{eng} + {tq}_{ISG}} )*\mu_{HTC}*i_{AT}*i_{Diff}} - {tq}_{Fahrwid}} \rbrack}{{theta}_{kfz}}{\mathbb{d}t}}}}$where:

-   -   μ_(HTC) is the increased torque provided by the hydrodynamic        torque converter    -   i_(AT) is the gear ratio of the automatic transmission    -   i_(Diff) is the gear ratio of the differential    -   r_(reifen) is the tire radius    -   theta_(kfz) is the moment of inertia of the vehicle and    -   tq_(Fahrwid) is the rolling resistance    -   (tq_(eng)+tq_(ISG))′ is the theoretical driving torque.

The required driving torque for the powertrain can be determinedaccording to the following equation

$( {{tq}_{eng} + {tq}_{ISG}} ) = {\frac{{tq}_{wheel}}{{slip}_{clutch}*i_{AMT}*i_{Diff}}*k_{pid}}$where:

-   -   i_(AMT)=i_(AT) is the gear ratio of the automatic transmission    -   i_(Diff) is the gear ratio of the differential    -   k_(pid) is the correction factor    -   slip_(clutch) is the clutch slip    -   tq_(eng) is the actual torque of the internal combustion engine    -   tq_(ISG) is the actual torque of the crankshaft        starter/generator    -   tq_(wheel) is the wheel torque.

The powertrain contains an additional power source and is provided witha control system which is used to produce a correction value for thepower source torque on the basis of a comparison of the real behavior ofthe powertrain with a modeled behavior of a powertrain provided with ahydrodynamic torque converter.

Practical developments of the invention are set forth in the sub-claims.The controlled power source is an internal combustion engine; theadditional power source is a crankshaft starter/generator (12), theclutch is implemented as an automatically operated friction clutch, andthere is provided a feedback control loop (21-27) which is used tosimulate the behavior of a torque converter.

The control system contains a conversion block which is used to converta required wheel torque to a crankshaft torque on the basis of thecorrection value, and a correction device in which the correction valuefor the torque is generated. It additionally has a torque divider whichis used to split the power source torque between the power source andthe additional power source. The control system also contains anobserver block which represents a model of a powertrain with ahydrodynamic torque converter and is used to calculate a vehicle speedcorresponding to the speed assumed by a comparable motor vehicleprovided with a hydrodynamic torque converter and automatic transmissionin response to the same driver input. The vehicle speed and the requireddriving torque for the powertrain are calculated using equations givenbelow.

The advantages of the invention are more specifically that thepowertrain is open-loop controlled by the driver input interpreted aswheel torque, and closed-loop controlled on the basis of the deviationbetween modeled and real vehicle behavior, thereby enabling the requireddrive characteristics to be achieved inexpensively. The advantageousstarting behavior of a conventional automatic transmission withhydrodynamic torque converter is achieved without the high cost andhigher fuel consumption necessary for a powertrain of this kind. Anadditional drive in the form of a crankshaft starter/generator is givenanother useful function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be explained with reference to theaccompanying drawings in which:

FIG. 1 shows a powertrain provided with a control system according tothe invention;

FIG. 2 shows a block diagram of a feedback control structure of thecontrol system according to FIG. 1,

FIG. 3 shows a block diagram for calculating the required power sourcetorque in the feedback control structure according to FIG. 2;

FIG. 4 shows a signal flow diagram of a model of the powertrainaccording to FIG. 1, and

FIG. 5 shows a correction block which is part of the feedback controlstructure according to FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A powertrain 1 of a motor vehicle (not shown) is controlled by a controlsystem 2 (FIG. 1). The powertrain and its control system comprise morespecifically a first power source in the form of an internal combustionengine 3, an engine control unit 4 which receives signals from a gaspedal 5, a friction clutch 6, an automated manual transmission 7(hereinafter also referred to as transmission), a clutch actuator 8 anda gearshift actuator 9 for the transmission 7. A superordinate controlunit 10, a so-called IPM control unit (IPM=Integrated PowertrainManagement), controls the engine 3 via the engine control unit 4, thefriction clutch 6 via the clutch actuator 8 and the automated manualtransmission 7 via the gearshift actuator 9.

The powertrain 1 also contains an additional power source in the form ofa crankshaft starter/generator 12 (hereinafter also referred to as ISG)which is used as both starter motor and generator. It is controlled byan ISG control unit 13 and is connected via same to an energy storagedevice 14 implemented here as a 42-volt battery. The control units 4,10, 13 and 14 are interconnected by a data transfer system in the formof a CAN bus 16 and can therefore exchange status messages, sensorsignals, commands and similar information with one another.

The additional power source can also consist of another auxiliary motor,e.g. an electric motor connected to the input shaft of the clutch 6 by abelt or chain.

As already mentioned, the purpose of the control system 2 is to realize,in the above described powertrain 1 without torque converter but havingan additional motor, the good starting behavior of motor vehicles with ahydrodynamic torque converter. This is achieved by modeling the responseto driver input of a powertrain with hydrodynamic torque converter.Actuation of the gas pedal 5 by the motor vehicle driver is interpretedas driver input.

From a comparison of a real behavior, i.e. in this case the behavior ofa motor vehicle with automated manual transmission and crankshaftstarter/generator, and of a modeled behavior, i.e. in this case thebehavior of a motor vehicle with hydrodynamic torque converter andautomatic transmission, a correction value or correction factor isdetermined which is used to convert the driver input to a torque at thecrankshaft (engine torque). The modeling is performed using observerfeedback control and is equivalent to calculating the behavior of amathematical model—the observer model—of the powertrain.

The driver input is regarded as “wheel torque based”, i.e. the driver'swish expressed by depressing the gas pedal is converted to a torquetransmitted by the wheels to the road and causing the desired vehiclemotion. The required wheel torque is back-calculated via the gear ratiosof the differential and of the transmission and via the correctionfactor to the value of the power source torque, i.e. in this embodimentthe value of the torque at the crankshaft.

The crankshaft torque is appropriately divided between the first powersource and the additional power source, i.e. the internal combustionengine 4 and the crankshaft starter/generator 12, and the two portionsare set by the engine control unit 4 and ISG control unit 13respectively. It is advisable, for example, to output the entire torquedemand to the engine control unit 4 until the maximum possible enginetorque for the relevant operating state is reached, and to transferexcess portions to the crankshaft starter/generator control unit 13.

A block diagram (FIG. 2) of the feedback control concept of the controlsystem 2 shows a circuit arrangement 18 comprising the following blocks.A block 19 “target wheel torque” receives the variables “driver input”,“speed” and “acceleration” as input signals 20 which are supplied bysensors or individual control devices in the motor vehicle, anddetermines from these input variables a target wheel torque, i.e. thevalue of the torque to be applied at the driving wheels of the motorvehicle. The term “block” is used here quite generally for a computing,analyzing, open- or closed-loop control device which can be implementedboth as a circuit and as a program.

The demanded torque is converted in a block 21 “Conversion” containingthe ratios of the various components of the powertrain 1, morespecifically of the differential and of the transmission, to a necessarytorque at the crankshaft of the engine 3. The calculation will beexplained further with reference to FIG. 3. The block 21 feeds out therequired crankshaft torque as an output variable, namely to a block 23“Observer” on the one hand and, on the other, to a block 24 “Torquedivider” as corrected crankshaft torque.

From the crankshaft torque calculated in the block 21, a vehicle speedV_(Model) is calculated in the “Observer” feedback control block 23.This block 23 represents a model of a powertrain with a torqueconverter, i.e. the vehicle speed V_(Model) corresponds to the speedwhich a comparable motor vehicle provided with a hydrodynamic torqueconverter and an automatic transmission would assume in response to thesame driver input. As the converter ratio is operating-point dependent,the observer contains a torque converter model which determines theengine RPM from the crankshaft torque and the turbine RPM(back-calculated from the speed). Static characteristics describing theproperties of the torque converter are used in the model.

The vehicle speed V_(Model) is applied to the positive input of asubtractor 26 whose output is connected to a block 27 “Correction”.Details of the speed calculation and torque division will be explainedwith reference to the following Figures.

The engine torque portions determined in the block 24, i.e. a setpointtorque for the crankshaft starter/generator and a setpoint torque forthe internal combustion engine, are transferred as output signals to thedrives of the real motor vehicle without torque converter, said vehiclebeing symbolized here by a block 28. The motor vehicle then moves at aspeed which is measured in the usual way and applied as measured valueV_(Fahrzeug) to the negative input of the subtractor 26.

The difference between calculated speed and measured speed istransmitted to the block 27. This block 27 generates a correction factork_(pid) and applies it to a second input of the block 21, therebycompleting a feedback loop for the correction factor k_(pid).

The conversion of the required wheel torque via the gear ratios of thepowertrain components to a required crankshaft torque in block 21 willnow be explained with reference to FIG. 3. The required wheel torque isfed via a first signal input 30 to the counter input of a divider 31.The correction factor k_(pid) is fed via a second signal input 32 to afirst input of a multiplier 34.

The variables clutch slip slip_(clutch), transmission gear ratioi_(Getr) and differential gear ratio i_(Diff) are fed as input signals35 to the inputs of a second multiplier 36 whose output signal is fed tothe denominator input of the divider 31 whose output signal is in turnfed out via a signal output 37 as uncorrected crankshaft torque, i.e.crankshaft torque required for a powertrain with automatic transmissionand hydrodynamic torque converter.

On the other hand the output signal is fed to a second input of themultiplier 34 where it is multiplied by the correction factor k_(pid)and then fed out via a signal output 38 as required crankshaft torquefor a powertrain with automated manual transmission AMT and crankshaftstarter/generator ISG. The output signal corresponds to the value of thefollowing equation:

$\begin{matrix}{( {{tq}_{eng} + {tq}_{ISG}} ) = {\frac{{tq}_{wheel}}{{slip}_{clutch}*i_{AMT}*i_{Diff}}*k_{pid}}} & ( {{Eq}.\mspace{14mu} 1} )\end{matrix}$where (see also Eq. 2):

-   -   α_(Fahrbahn) is the angle of gradient (e.g. measured using a        sensor)    -   μ_(HTC) is the increased torque due to the HTC (observed        variable)    -   a_(Fahrzeug) is the vehicle acceleration (calculated)    -   i_(AMT)=i_(AT) is the gear ratio of the automatic transmission        (assumed to be constant for the relevant gear)    -   i_(Diff) is the gear ratio of the differential (assumed to be        constant)    -   k_(pid) is the correction factor    -   r_(reifen) is the tire radius (assumed to be constant)    -   slip_(clutch) is the clutch slip    -   theta_(kfz) is the vehicle's moment of inertia (assumed to be        constant)    -   tq_(Eng) is the actual torque of the internal combustion engine        (measured via the data bus)    -   tq_(Fahrwid) is the rolling resistance as f(V_(Fahrzeug) and        angle α_(Fahrbahn))    -   tq_(ISG) is the actual torque of the ISG (measured via the data        bus)    -   tq_(wheel) is the wheel torque    -   V_(Fahrzeug) is the vehicle speed (measured)    -   V_(Model) is the vehicle speed (calculated)

The signal flow diagram 40 shown in FIG. 4 corresponds to thecalculation of the speed V_(Model) from the crankshaft torque in theblock 23 “Observer”. The crankshaft torque is fed via a signal input 41to a first input of a block 42 mathematically simulating thehydrodynamic torque converter, namely as engine torque present at thepump impeller of the torque converter. The second input of the block 42is connected to the output of a multiplier 43 in which the followingvalues are multiplied by the driving angular velocity of thehydrodynamic torque converter: the transmission gear ratio, thedifferential gear ratio and the angular velocity of a driven wheel.

From an output, the block 42 applies the value of the torque Tq_turbineat the turbine impeller to an input of a multiplier 44 at whose otherinputs the values transmission gear ratio and differential gear ratioare likewise present. The product of the three input values is fed tothe positive input of an adder 45.

In a block 46 “Rolling resistance”, the negative moment of resistancetq_Fahrwid caused by the rolling resistance is determined from thesensors or otherwise recorded values of the road gradient and speed ofthe motor vehicle and is applied to a negative input of the adder 45from whose output the resulting effective wheel torque is applied to thecounter input of a divider 48.

From a block 50 “Inertia”, the mass inertia theta_kfz, namely therotatory and translatory inertia of the motor vehicle, is fed to thedenominator input of the divider 48 where the time derivative of theangular velocity of the wheel is determined and fed to an integrator 51which calculates therefrom the angular velocity of the wheel and passesit to an input of a multiplier 52 to whose second input the wheel radiusvalue is fed from a memory 54. From the two input values, the multiplier52 calculates the speed of the vehicle and feeds it out via an output55. The signal fed out here corresponds to the value of the followingequation

$\begin{matrix}{V_{Fahrzeug} = {r_{reifen}*{\int{\frac{\lbrack {{( {{tq}_{eng} + {tq}_{ISG}} )^{\prime}*\mu_{HTC}*i_{AT}*i_{Diff}} - {tq}_{Fahrwid}} \rbrack}{{theta}_{kfz}}{\mathbb{d}t}}}}} & ( {{Eq}.\mspace{14mu} 2} )\end{matrix}$where (tq_(eng)+tq_(ISG)) is the theoretical required torque, i.e. thedriving torque demanded by the driver, in contrast to the manipulatedvariables of the powertrain 1 that have to be adapted by the correctionfactor from the required torque calculation. The meaning of the otherformula variables is explained above under equation Eq. 1. The notationstheta_(kfz) and theta_kfz, etc. are equivalent here: the former issuitable for mathematical formulae, the latter for computer programs.

Details of the hitherto schematically illustrated block 27 “Correction”are shown in FIG. 5. A PID controller receives the speed deviationV_(Model)-V_(Fahrzeug) via a signal input 58 and then generates acontrol output which is additively combined with an offset value in anadder 60. The offset value is used to match the control output producedby the PID controller to the gain values of the hydrodynamic torqueconverter. It has, for example, the numerical value one. The sum formsthe correction factor k_(pid) and this is fed out via an output 62,namely as mentioned to the block 21 “Conversion” (see FIG. 2). It formsthe manipulated variable and is incorporated as the gain factor in thecalculation of the required crankshaft torque for the powertrain 1. Thiscrankshaft torque value is transferred to the real powertrain as thesetpoint target.

Comparison of the acceleration behavior of a vehicle with hydrodynamictorque converter and automatic transmission and a vehicle with automatedmanual transmission and crankshaft starter/generator shows—for the samegas pedal pressure and the same crankshaft torque, i.e. without thecorrection described above—that the powertrain with torque converterallows a much higher vehicle acceleration because of the increasedtorque provided by the torque converter.

On the other hand, comparison with a powertrain having automated manualtransmission and crankshaft starter/generator and having the describedcrankshaft torque control shows—with the same gas pedal setting—thatthis vehicle has an acceleration behavior approximately corresponding tothat of a vehicle with hydrodynamic torque converter.

1. A motor vehicle powertrain comprising: a controlled power source; aclutch; an automatically shifted transmission without a hydrodynamictorque converter; a data transfer system enabling data to be exchangedbetween the component parts of the powertrain; an additional powersource distinct from the controlled power source; and a control systemfor producing a correction value for the power source torque on thebasis of a comparison of the real behavior of the powertrain with amodeled behavior of a powertrain provided with a hydrodynamic torqueconverter; wherein the control system controls the additional powersource to provide additional torque depending on said correction value,such that the additional torque provided by the additional power sourceis combined with the torque provided by the controlled power source toprovide a greater torque than can be provided by the controlled powersource alone, and such that for a particular gas pedal setting, theadditional torque provided by the additional power source approximatelycorresponds to the increased torque provided by the hydrodynamic torqueconverter of the modeled powertrain at the same particular gas pedalsetting.
 2. The powertrain according to claim 1, wherein the controlledpower source is an internal combustion engine; the additional powersource is a crankshaft starter/generator, the clutch is implemented asan automatically actuated friction clutch, and there is provided afeedback loop for simulating the behavior of a torque converter.
 3. Thepowertrain according to claim 2, wherein the control system contains aconversion block for converting a required wheel torque to a crankshafttorque on the basis of the correction value, and a correction device inwhich the correction value for the torque is generated.
 4. Thepowertrain according to claim 1, wherein the control system contains aconversion block for converting a required wheel torque to a crankshafttorque on the basis of the correction value, and a correction device inwhich the correction value for the torque is generated.
 5. Thepowertrain according to claim 1, wherein the control system has a torquedivider for splitting the power source torque between the power sourceand the additional power source.
 6. The powertrain according to claim 1,wherein the control system has an observer block which represents amodel of a powertrain having a hydrodynamic torque converter and is usedto calculate a vehicle speed corresponding to the speed assumed by acomparable motor vehicle provided with a hydrodynamic torque converterand an automatic transmission in response to the same driver input.
 7. Amethod for controlling powertrain comprising a controlled power source,a clutch, an automatically shifted transmission without a hydrodynamictorque converter and a data transfer system enabling data to beexchanged between the component parts of the powertrain, an additionalpower source distinct from the controlled power source, and a controlsystem comprising the steps of: producing a correction value for thepowertrain torque on the basis of a comparison of a real behavior of thepowertrain without a hydrodynamic torque converter with a modeledbehavior of a powertrain provided with a hydrodynamic torque converter,controlling said additional power source to provide for an additionaltorque depending on said correction value, such that the additionaltorque provided by the additional power source is combined with thetorque provided by the controlled power source to provide a greatertorque than can be provided by the controlled power source alone, andsuch that for a particular gas pedal setting, the additional torqueprovided by the additional power source approximately corresponds to theincreased torque provided by the hydrodynamic torque converter of themodeled powertrain at the same particular gas pedal setting.
 8. Themethod according to claim 7, wherein a conversion block performs aconversion of a required wheel torque to a powertrain torque on thebasis of the correction value and that the powertrain torque is dividedbetween the power source and the additional power source.
 9. The methodaccording to claim 8, wherein a demanded torque is converted to anecessary torque at the crankshaft of the power source using the gearratios of the powertrain components.
 10. The method according to claim7, wherein a demanded torque is converted to a necessary torque at thecrankshaft of the power source using the gear ratios of the powertraincomponents.
 11. The method according to claim 7, comprising the step ofsplitting the power source torque between the power source and theadditional power source by a torque divider.
 12. The method according toclaim 7, comprising the steps of: representing a model of a powertrainhaving a hydrodynamic torque converter by an observer block and usingthe model to calculate a vehicle speed corresponding to the speedassumed by a comparable motor vehicle provided with a hydrodynamictorque converter and an automatic transmission in response to the samedriver input.